Manufacture of sodium thiosulphate



' l n 1,639,905 F. w. SPERR, JR., ET AL MANUFACTURE 0F' S ODIUM THIOSULPHATE Aug. Z3,A 1927.

Filed April 4,v 1921 D am Jomfbzy@ 'EN -f I y G Lama-2d mi?, me PUMP To as 50u55# .75m/52712721' VMM 7% Patented Aug. 23, -19275'v UNITED STATE-s,

AparENT oFFIcE.

FREDERICK W. SPERR, JR.,"AND DAVID L. J'ACOBSION,` OE PITTSRURGH, PENNSYL VANIA,l A'SSIGNORS TO THE v'KOPPERS COMPANY, A i CORPORATION OF PENN' 'sYLvANIa Application mea Ap'ril 4,

This inventionI relates to the production of alkali metal thiosulphates, such for exam- 1 ple as sodium thiosulphate. "The invention has Jfor an' object to eliect the production of such thiosulphates by the* utilization of hydrogen sulphide in gases contaimngit. Ex-

amples. ot such gases are: coke oven gas prior to its `subjectionto a gas purifying process, carbureted "Water gas and gases from petroleumv distillation. lBy the invention the hydrogen sulphide, which is lthe principalA Waste product' in such gases, vis

, conserved, being converted intov a valuable A part of this specification, and showing,

purposes of 'exemplicatiom a 'preferred form and manner in which the invention may be embodied and practiced, but without I proved thiosulphate process of the present invention.

limiting the claimed invention specifically to. such illustrative instance or instances, v'the ligure illustrates a diagrammatic representa-- tion of apparatus for carrying out the im- .ln its present embodiment, the invention l is applied to the production of sodium thio- 1 valuable applications, for' exampl'eto the sulphate, and, for convenience,'the 'present` description Will be confined to this'use ofthe invention. The features.- of the invent1on are; however, readily suseptible of other production of other alkali metal thiosulphates such as potassium thiosul hate; consequently the scope of the inven ion is not confined to the specific use and specific embodiment herein describedas -anillustrative example.

For leffecting' the absorption of sulphur' -compoun'dsfrom the gas and the'subsequent formation of thiosulphate, there is employed a water solution of an alkaline compound having an anity for hydrogen sulphide. vA number of 'the compounds of the alkali metals andvalkali earth-metals possess this I propertyl- However, according tothe present embodiment of the invention, a' solution of alkaline sodium compound `in water is j lu'alvurncTURB oF soDIUM TEISULPHATE.

1921. serial No. 458,265.`

employed. vExamples of such compounds 'are sodium carbonate, sodium bi-carbonate,

sodium sulphide and sodium hydroxide or various mixtures of the above mentioned sodium compounds. A solution of sodium carbonate in Water is' especially suitable for effecting the absorption of the sulphur from the gas, and assuming that this be the absorbent agent employed, the` sodium carbonate solution is brought into contact With the gas containing hydrogen 'sulphide in' a suitable apparatus whereupon the hydro en sul.

phide is absorbed from the gas forming sulphur compounds in the solution. The solut1on contaming the absorbed sulphur Icompounds is'thenbrought into contact with air or other gases containing oxygen. This aeration liberates part of the hydrogen sulphide from the solution, but a portion. of the sulphur compounds'areoxidized tothiosulphate", such as sodium thiosulphate. On

again subjecting. the thus aerated solution to contact with additional gasfcontaining hydrogen sulphide, Lfurther vquantities of sulphur yare absorbed vand from subsequent aeration vadditional thiosulphateis formed; and the process' is preferably carried on continuously so `that the. solution is continuously brought Yinto contact vwith the gas and subsequently aerated The sodium thiosulphate centration, forexample up to about the saturation point for sodium thiosulphate. -Additional amounts of the alkaline sodium compounds are added tothe solution from time to time-to replace the sodium that is transformed into" thel thiosulphate.

Whenthe solution shows the desired concentration of thiosulphate, a portion of the solutionmay 'be .drawno'i fromthe system Aand the sodium thiosulphate lis separated from the othersodium salts and'recovered, -for example, by the process forthe recovery The formation of thiosulphate may be considerably accelerated by heating the solution just before the aeration stage or during the aeration stage. When such heating .is employed vit is preferable to coollille solution before bringingit lback into contact with the -gascontaining the hydrogen sulphide; in-

is very solubleran'd accumulates in solution, f which may be brought up to any desired confof sodium thiosulphatefrom solutions such as are -described in the co-pendingapplicamost cases, however,t the solutionA will be cooled sufliciently by the aeration itself.

In applying the above,stated discovery to the production of sodium thiosulphate from a gas, such as coke oven gas, a concentration of about 2 to 5 per centum of sodium carbonate inthe absorbent solution will be found satisfactory. Sodium carbon- 7emerges from the scrubber `pipe I.

l The sodium carbonate solution containing the absorbed sulphur passes out of the scrub- .ber through a discharge line VJ- to a circulating' tank A, in which it is preferable toheat ,the solution. Such heating .may be effected by meansv of steam coils R placed in the tank A 'or steam may be blown directly into the, solution in the tank. A s hereinabove stated `the heating acts to accelerate the formationV of sodium thiosulphate in the solution. From the circulating tank A,the solutlon'is pumpedby a pump K through the pipe line -L' over the aerating tower M, which may be still another scrubber, similar to the scrubber C or may be a natural draft cooling tower in which'the solution'is aeratedl by being brought into -contact with the atmosphere under natural draft. In the present instance, hbwever, the drawing shows` a scrubber type of apparatus .into which air is blown by means ofthe fan N. The air together with quantities of IIZS given up from the solution,` passes `out of the aerating tower through the pipe O. From the aeratino` tower the .aerated solution containing sozdium thiosulphate runs through the pipe. P into a circulating tank B, where the solu tion ma be mixed with fresh sodium carbonate lrom the storage bin Q, in suicient quantities to maintain they solution at approximately constant alkalinity. From the circulating tank B the solution is pumped p scrubber C, where it is again'brought intoi contact with the -gas containing hydrogen sulphide,for the .further absorption of sulphur and the further yformation ofsodium thiosulphate. .Y When the sodium thiosulphate has 'accumulated to a desired percentage in the solution, for example to about 10% of the solution',I the valve F is openedand a por. tion ofthejsolution is transferred into the storage tank E. The remaining solution in the circulating systemv is made up 'to its original volume bythe addition of fresh water, and lsodium carbonate from the bin Q. to maintain constant alkalinity. It is y preferablefbefore transferring the solutionf .from the circulating system into the stor-. age tank E to discontinuev temporarily the addition of fresh sodium carbonate until the percentage of the sodium carbonatey in the circulating 'solution is reduced to about 1 or 2 per centum. This will eliminate the separation and handling of a considerable amount of sodium carbonate in the subsequent treatment, of the solution transferred to the storage tank E After withdrawing the solution into the storage tank', .howeyer, the remaining solution should be at once re` stored to its original volume and alkalinity.

The solution in the storage tank E, con` taining the sodium thiosulphate may then be treated for the recovery of thev sodium thiosulphate in pure form, for example, according' to the process described in the aforea,

said' co-pending application of R. E. Hall and D..L. Jacobson.,

By the invention the hydrogen sulphide is removed from the gas, thereby eliminating this objectionable impurity in vases, and the commercially valuable thiosulphate of a h1gh degree of purity is formed. When recovered from the solution, the crystallized product.4 has five molecules of water of crystallization according to lthe formula Na2S2O3.5H2O.

The invention as' hereinabove set forth maybe variouslyI embodied within the scope of the claims hereinafter made.

We claim: j

1. In a process for the production of alkali metal thiosulphate, the combination of steps that consists'in: passing gas containing hydrogen sulphide through an alkaline solution to 'absorb the hydrogen sulphide from the gas; subjecting the -solution to such heating and aeration as tc effect the formation of the alkali netal thiosulphate; and withdrawing from the circulating system solutionfor the recovery of the alkali metal thiosulphate,

when the latter has accumulatedin the system to aboutv ten per centum of the total volume of the solution.

2. In a process for the production of so-l l -dium thiosulphate, the combination of steps by a pump G through therlme lD back to the that consists in: passing a gas containing hydrogen sulphide through sodium carbonate` solution to absorb the hydrogen sulphide from the gas; :subjecting the solution to such heat1ng and aeration as to effect the .formatlon of the sodium thiosulphate; and

3. In a process for the production of alkali metal thiosulphate the combinat-ion of steps that consists in: passing a gas containing hydrogen sulphide through an alkaline solution to absorb the hydrogen sulphide'from the gas; heating and treating the solution oontaining the absorbed hydrogen sulphide with an oxidizing agent so as to eect the formation of the alkali metal thiosulphate; and withdrawing from the circulating system solution for the recovery of the alkali metal thiosulphate, when the latter has accumulated to about its saturation point in the system.

4. .In a process for the productibn of alkali metal thiosulphate, the continuous cyclic circulation of an alkali solution through ahydrogen sulphide absorption stage in which the solution absorbs hydrogen sulphide from.

iphide.v

ahydrogen sulphide bearing gas, continued with the continuous heating and-aeration of metal salt to the solution in the circulating system to restore the solution to its original alkalinity for absorption of hydrogen-sul- In testimony whereof We have hereunto 'set our hands.

FREDERICK4 W.v SPERR, JR. DAVID L. JAooBsoN. J

the cyclically-circulatingsolution discharged 

